Unhappy Error: Memory Card Not Found

A few months ago (around March), I bought a refurbished HTC 7 Mozart, and up until today it's been working absolutely perfectly. This morning, I noticed my phone was off, and when I turned it on, I was greeted with the message "Memory card not found", followed by some text saying that I need to replace the card...

I initially tried a factory reset by pressing both volume keys on the boot screen to no luck. I then followed Andy Hamilton's guide to replacing the micro-sd card, After removing it, I tried reading it with my PC, but it wouldn't detect it, therefore I replaced it with another one (Kingston 8Gb Series 4).

After starting up the phone again and doing a factory reset, it initially worked, the phone prepared itself and all appeared to be working perfectly until I went to access my wifi network. I soon as I typed in my router's password and pressed confirm, the phone freezed up and crashed. It then went back to being like before, and factory resetting it won't repair it, nor is the phone recognised in Zune so I can't restore a back-up. What to do I do know?